To satisfy power supply and dynamic requirements of today's microprocessors and related communication systems, many approaches have been implemented. Single-phase voltage-mode hysteretic control, also called “bang—bang” control or ripple regulator control, typically maintains an output voltage within a hysteresis band centered about an internal reference voltage. If the output voltage reaches or exceeds the reference voltage plus one-half of the hysteresis band, the controller turns OFF the high-side switch, which can be a Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET), and turns ON the low-side switch, to block energy from being transferred from an input to an output. This latter condition is a power stage OFF-state, and causes the output voltage to decrease.
When the output voltage is at or below the level of the reference minus one-half of the hysteresis band, the power stage goes into ON-stage, and the controller turns ON the high-side switch, and turns OFF the low-side switch to allow energy transfer from the input to the output, which causes the output voltage to increase. This hysteretic method of control keeps the output voltage within the hysteresis band around the reference voltage. Thus, an output voltage of one volt is generally corrected from a deviation as small as a few millivolts as quickly as an output filter allows.
In an ideal hysteretic control circuit, an output voltage is typically regulated into a hysteresis band and a DC value of the output voltage is equal to a reference voltage, hence there is no DC error. A significant benefit of hysteretic control is its fast response. If an output-load current step or an input-voltage transient forces the output voltage out of the hysteresis band, the control circuit may set a power-stage MOSFET in a continuous on or off state as required to return the output voltage back to the hysteresis band. Thus, the output voltage may be corrected as quickly as an output filter allows. Generally, there are no delays from an error amplifier and its associated feedback loop as there are in voltage- and current-mode controllers. Other advantages of hysteretic control include no feedback-loop compensation and no input filter interaction problems. Thus, hysteretic control is a relatively inexpensive and simple regulation architecture.
Commonly used hysteretic control circuits have poor regulation accuracy, however. Typically inaccuracies up to 30 mV are not uncommon. For applications such as microprocessors, where accuracies exceeding 20 mV may not be acceptable, poor regulation accuracy of a hysteretic control circuit may make it undesirable although its fast response and robustness may make it attractive. To overcome the propagation delay's influence and to improve hysteretic control circuit's accuracy, typically circuits may be over-designed, resulting in increased cost and sacrificed performance.
Thus, it is with respect to these considerations and others that the present invention has been made.